class_docstr: test layout templates
code: def test_size_to_css(self):
      box = widgets.AppLayout()
      assert box._size_to_css("100px") == "100px"
      assert box._size_to_css("1fr") == "1fr"
      assert box._size_to_css("2.5fr") == "2.5fr"
      assert box._size_to_css("2.5") == "2.5fr"
      assert box._size_to_css("25%") == "25%"
  
      with pytest.raises(TypeError):
          box._size_to_css("this is not correct size")
  
imports: from unittest import TestCase
  import pytest
  import traitlets
  import ipywidgets
  from ipywidgets.widgets.widget_templates import LayoutProperties
label_desc: Use image node_id 3 for calling the TestAppLayout obj's underlying member method code with example usage: obj.test_size_to_css() without return types